Power transmission lines carrying electrical power are often suspended above a ground surface using a series of utility poles or other elevated support structures. In order to prevent the utility pole from being energized and grounding or shorting the power lines, insulated framings are used to insulate the energized power lines from the supporting pole or other structure. Common framings used in the power industry include wooden or metal cross-arms or brackets. Power line conductor or cables are mounted to various points on the structures, cross-arms or brackets and separated from direct contact with the structures, cross-arms or brackets by insulators, which are components constructed from non-conductive materials such as fiberglass, polymers, and ceramics.
Common configurations for insulators mounted to framings include vertical insulators extending either upward or downward from the cross-arm or the top of the utility pole, and horizontal insulators extending to the left or right of the support structure, ends of the cross-arm, or brackets. The insulators usually have base fittings that are mounted on the structure, cross-arm or brackets. The end of the insulator distant from the structure, cross-arm or bracket is usually fitted with a clamp or other support device to hold a power line in place: horizontally-mounted insulators use a horizontally-oriented clamp or other support device, while vertically-mounted insulators use a vertically-oriented clamp or other support device.